What is the sentence for word at?

The word "at" doesn't have a single sentence. It's a preposition, so it needs to be used within a sentence.

Here are some examples:

* I am at the park.

* The meeting is at 3 pm.

* She is good at playing the piano.

* He was looking at the stars.

As you can see, "at" is used to show location, time, or a specific point.